1. Field of the Invention
The invention relates to a motor control device for controlling a motor and a generator control device for controlling a generator.
2. Description of Related Art
There has been proposed a system that controls a motor by estimating torque being generated at the motor and controlling the motor by using the estimated torque.
In this type of system, torque generally is estimated by computing an exterior product of a flux-linkage vector of the armature winding provided at a stator and a current vector of the current flowing at the armature winding (see Japanese Patent Laid-Open No. 2003-210000 and Japanese Patent Laid-Open No. 7-298696). There also has been proposed a method to estimate torque from input electric power information to a motor and rotating speed information of the motor (see Japanese Patent Laid-Open No. 2005-102467).
Now, when a synchronous motor with embedded magnets is used as a motor, there often exist harmonic in the magnetic flux distribution of the magnet with respect to the magnetic pole position (rotor position) and in the inductance distribution. In other words, for example the flux of the permanent magnet linked to the U-phase armature winding of the stator ideally has a sinusoidal wave pattern with respect to the positional changes of the magnetic pole, but in reality, such a wave pattern includes the harmonic, which also causes distortion in the induced voltage generated by the rotation of the permanent magnet. Similarly, d-axis inductance and q-axis inductance of the armature winding also include the harmonic. It is known that such harmonic becomes a cause of torque ripple.
In the conventional torque estimation methods as the ones described above, this fluctuation component of the torque (torque ripple) cannot be estimated well. As a result, the error between an instantaneous value of the estimated torque and an instantaneous value of the actual torque increases and the motor control deteriorates from what is ideal. Reasons that the fluctuation component of the torque cannot be estimated well in the conventional torque estimation methods will be described below. In addition, while the conventional problem relating to the motor control was explained, similar problem occurs when controlling a generator.
Thus, the invention aims to provide a motor control device that can estimate the fluctuation component of the torque generated at the motor well, and a generator control device that can estimate the fluctuation component of the torque generated at the generator well.